635.    CRANGLE, J., AND SUCKSMITH, W.  Magnetic Analysis of Iron-Carbon Alloys.  Tempering of Martensite and Retained Austenite.  Jour. Iron Steel Inst. (London), vol. 168, 1951, pp. 141-151; Chem. Abs., vol. 45, 1951, p. 6559.

      Pure Fe-C alloys were austenitized and quenched to convert them to martensite.  Magnetic analysis indicates that hexagonal Fe carbide is present in the 1^st tempering stage (100° C.); its Curie point may be considerably lower than 380° C., and its composition may differ from Fe₂C.  The 2d tempering stage (150°-200° C.) is characterized by the absence of retained austenite (which decomposes into the same products that were formed in the 1^st stage) and by the appearance, above 200° C., of a small amount of cementite.  The shapes of the thermomagnetic curves of specimens in the 3d stage (250°-350° C.) suggest the presence of a carbide with properties similar to Hägg carbide. To eliminate this carbide completely, the temperature must be raised above 500° C, where the only remaining carbide is cementite.